Debugging LIBPF applications with gdb

GNU debugger (gdb) is the standard command-line debugger on many Unix-like systems for troubleshooting C++ programs.

To prepare for debugging your application, compile it with debugging symbols enabled; for example assuming you want to debug Qpepper and use bjam to build:

cd ~/LIBPF/pepper
bjam debug Qpepper

or if you use qmake/make to build:

cd ~/LIBPF/pepper
qmake
make debug

A typical debugging session starts by launching gdb with the relative path to the executable as a parameter:

cd ~/LIBPF/bin
gdb ./pepper/gcc-4.9.2/debug/Qpepper

Next we typically want to set up a breakpoint at the Error::Error function, which is where the control flow will pass if an exception is thrown; to do that, use the b (breakpoint) command:

b Error::Error

Then you launch your application with the required command-line parameters with the r (run) command:

r new jjj

When the exception is thrown, the debugger will stop at the breakpoint:

Breakpoint 1, Error::Error (this=0xed2080, 
    cf=0xa03dc0  "Node* NodeFactory::create(std::string, Libpf::User::Defaults, uint32_t, Persistency*, Persistent*, Persistent*)") at ../utility/src/Error.cc:56
56      Error::Error(const char *cf) : msg_("Error was thrown by function: ") {

From here you can:

  1. examine the call stack with the where command, which will return something like:
    #0  Error::Error (this=0xed2080, 
        cf=0xa03dc0  "Node* NodeFactory::create(std::string, Libpf::User::Defaults, uint32_t, Persistency*, Persistent*, Persistent*)") at ../utility/src/Error.cc:56
    #1  0x00000000006097b2 in ErrorObjectFactory::ErrorObjectFactory (this=0xed2080, 
        cf=0xa03dc0  "Node* NodeFactory::create(std::string, Libpf::User::Defaults, uint32_t, Persistency*, Persistent*, Persistent*)", ty=0xed09e8 "type jjj not found")
        at ../utility/src/Error.cc:117
    #2  0x00000000007d30c1 in NodeFactory::create (this=0x7fffffffd7ef, type="jjj", defaults=..., id=0, 
        persistency=0x0, parent=0x0, root=0x0) at src/NodeFactory.cc:57
    #3  0x00000000004263ec in createCase_ (type="jjj", defaults=..., error=@0x7fffffffdffc: 32767, svgs=true)
        at src/Kernel.cc:228
    #4  0x0000000000427901 in Libpf::User::createCase (type="jjj", tag="jjj", description="", jcd="", 
        error=@0x7fffffffdffc: 32767) at src/Kernel.cc:317
    #5  0x000000000040e64d in main (argc=3, argv=0x7fffffffe158) at ../user/src/main.cc:189
    

    notice the first column that is the frame number, and the error message details found as ty parameter to the function call in frame #1: type jjj not found

  2. jump to the frame that occurred in your own code and not in the library, such as frame #5, using the f (frame) command:
    f 5
    
  3. list the source code around the current execution point with the l (list) command, which will return something like:
    189         Libpf::User::Handle caseHandle = Libpf::User::createCase(type, tag, description, options, error);
    (gdb) l
    184         std::string options("");
    185         if (argc > 5) {
    186           options = argv[5];
    187         } // if options are passed
    188
    189         Libpf::User::Handle caseHandle = Libpf::User::createCase(type, tag, description, options, error);
    190         if (error < 0)
    191           quitNow(error);
    192         else
    193           quitNow(caseHandle.id());
    (gdb) 
    

Issuing the same commands repeatedly at the gdb command prompt is common, therefore it’s handy to enable gdb command history:

cat >> ~/.gdbinit
set history save
set history filename ~/.gdb_history
^d

For more debugging tips, check the excellent RMS gdb tutorial or the gdb manual.

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Summary of the A&T fair, 2016 edition

Here is the Affidabilità e Tecnologie (A&T) fair, 2016 edition (held in , Torino April 20-21 2016) summarized by three audiovisual documents:

  1. Robot drives train:
  2. Robot plays golf:
  3. Robot brews coffee:
    WP_20160421_010
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Bash on Windows 10

This week at Build 2016, the yearly developer-oriented conference, Microsoft announced that Windows 10 will be able to run Linux’s Bash shell, by executing the native Ubuntu binary as-is.

Don’t stop at the news headline though: this is not just about Linux Bash, the command shell and scripting language.
All Ubuntu user space commands can potentially work, including the apt package manager with which you can tap from the 60000+ software packages available in the Ubuntu repos.

More technical details are found in two blog posts by Dustin Kirkland, an Ubuntu employee that worked with Microsoft on the magic behind.

This is no virtualization / container technology. It is more about API emulation: Linux system calls get translated in real time into Win32 API calls. No need to recompile the binaries.

P488

It’s an approach that resembles the POSIX subsystem that was part of Windows NT, whose latest (2004) denomination was “Subsystem for UNIX-based Applications” (SUA), deprecated with Windows 8 and Windows Server 2012 and completely removed in Windows 8.1 and Windows Server 2012 R2. I guess it its just a resurrection of this approach.

Even if this technology is aimed at developers, if you think about it, it has certain strategic implications.

On the Operating System competition landscape, this levels the field with Apple OS X, which already had Bash and several package managers (but not apt ! and the binaries had to be recompiled !). It is a praise to the outstanding technical excellence of the Debian Linux distribution, which lies at the foundation of Ubuntu. It lowers the attractiveness of Linux on the Desktop, as developers can run all their preferred tools from within Windows. It lowers the barriers against migrating to Windows services and solutions developed on Linux technologies and stacks (MAMP, LAMP …): not that this wasn’t possible before, but you had to depend on many more bits and pieces of uncertain trust-wordiness. Now it looks like a simpler and well supported path.

It obsoletes certain technologies designed for similar purposes such as Cygwin and MinGW. It also obsoletes the plethora of ad-hoc installers and Windows-specific binaries for tools such as ActivePerl, git, PostgreSQL, nginx, Ruby, Node.js et cetera.

Finally, on the Open Source / commercial software divide, it demonstrates once more (should there be any need for it) that business can benefit from Open Source: effective immediately, thousands of Open Source enthusiasts are working for the good of Microsoft, with no compensation.

ATM many questions are still open: when will this technology land on Windows Server (currently it requires to install an app from the Windows Store, which is not always possible) ? Will this be available on previous versions of Windows like Windows 7 and 8.1 ? Will this be integrated with system administration tasks such as installing / un-installing a service ?

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Modeling a pipe with a large pressure drop

The Pipe model is a concentrated parameter model for pipes. The correlations it uses are applicable only for small pressure drops, i.e. less than 10% of the absolute inlet pressure. If the calculated pressure drop is larger than that, you’ll get a warning.

But what to do if you have a long pipe or a pipe with a large pressure drop ?

Pipes by Nigel Howe

Pipes by Nigel Howe


The solution is to use a MultiStage unit to put together a number of Pipe units in series, thereby effectively discretizing the unit.

Assume this is your flowsheet definition (in the constructor):

addUnit("Pipe", defaults.relay("DN300", "connection piping"));
// ...

addStream("StreamLiquid", defaults.relay("S03", "inlet flow"), "RX", "out", "DN300", "in");
addStream("StreamLiquid", defaults.relay("S04", "outlet flow"), "DN300", "out", "BD", "in");

and this is the pipe unit data (in the setup method):

Q("DN300.de").set(300.0, "mm");
Q("DN300.s").set(5.0, "mm");
Q("DN300.L").set(2000.0, "m");
Q("DN300.h").set(0.0, "m");
Q("DN300.eps").set(0.0457, "mm");
Q("DN300.vhConcentrated").set(3.0 * 0.75);

(beware this is C++ code ! check a tutorial if you have no clue how process modeling in C++ is possible !)

So to discretize the Pipe unit you’d merely change the addUnit command creation to create a MultiStage unit (no need to change the addStream statements):

addUnit("MultiStage", defaults.relay("DN300", "connection piping")
  ("nStreams", 1)
  ("typeT", "Pipe")
  ("typeU", "StreamLiquid")
  ("nStage", 30));

The meaning of the options passed to the addUnit command and ultimately to the constructor of the MultiStage unit is:

  • nStreams: this is useful for more complex multi-stream arrangements, in this case each Pipe unit has just one inlet and one outlet so we set it to 1
  • typeT: the type of the unit operation model used for each “stage”
  • typeU: the type of the stream model which connects the “stages”.
  • nStage: the number of stages i.e. of discretization steps

The model setup becomes:

for (int j=0; j< I("DN300.nStage"); ++j) {
  std::string stage("DN300:S[" + std::to_string(j) + "]");
  at(stage).Q("de").set(300.0, "mm");
  at(stage).Q("s").set(5.0, "mm");
  at(stage).Q("L").set(2000.0 / static_cast<double>(I("DN300.nStage")), "m");
  at(stage).Q("h").set(0.0, "m");
  at(stage).Q("eps").set(0.0457, "mm");
  if (j == 0)
    at(stage).Q("vhConcentrated").set(3.0 * 0.75);
}

Here we iterate over all the “stages” and set de (external diameter), s (thickness), h (elevation) and eps (rugosity) to the same values as before on all discretization “stages”; the L (length) we divide by the number of “stages”; finally the vhConcentrated (velocity heads associated to the concentrated pressure drops) we place only once in the 1st “stage”.

Done !

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Where is the SQL database plugin for ODBC (qsqlodbc.dll) in Qt 5.6 ?

It looks like the SQL database plugin for ODBC (qsqlodbc.dll) is missing from the standard Qt 5.6 installer for Windows you download from http://www.qt.io/download-open-source.

You’d expect to find it in C:\Qt\Qt5.6.0\5.6\msvc2015_64\plugins\sqldrivers\ where the sqlite, mysql and postgresql ones are found, but the ODBC plugin is not there.

The issue is known (see QTBUG-49420 and QTBUG-51390) but these bug reports are closed and it seems there will be no fix on a short term.

So here is how you build qsqlodbc.dll from source for Windows 64-bit with Visual Studio 2015, based on the instructions “How to Build the ODBC Plugin on Windows”.

First get the source package qt-everywhere-opensource-src-5.6.0.zip from
http://download.qt.io/archive/qt/5.6/5.6.0/single/ and unzip it in any location, for example C:\qt-everywhere-opensource-src-5.6.0.

Now open a “VS2015 x64 native tools command prompt”, CD to the location of the qt-everywhere-opensource-src-5.6.0 directory then:

cd qtbase\src\plugins\sqldrivers\odbc
C:\Qt\Qt5.6.0\5.6\msvc2015_64\bin\qmake odbc.pro
nmake

At the end you’ll find the qsqlodbc.dll in C:\qt-everywhere-opensource-src-5.6.0\qtbase\plugins\sqldrivers alogside with qsqlodbcd.dll and qsqlodbcd.pdb.

Just copy these three files to the location where the Qt 5.6 installer for Windows should have put them
C:\Qt\Qt5.6.0\5.6\msvc2015_64\plugins\sqldrivers\ and you’ll be done !
sqlodbc

Posted in C++, Howtos, Rants | 1 Comment

“api-ms-win-crt-runtime-l1-1-0.dll is missing” error with LIBPFonOPC on Windows Server 2012 R2 64 bit

You may receive the error “The program can’t start because api-ms-win-crt-runtime-l1-1-0.dll is missing” when launching the LIBPFonOPC configurator 1.0. 2264 on a fresh install of Windows Server 2012 R2 64 bit.

01Related symptom: this error silently appears in the Setup Log of the Event viewer during the installation of LIBPFonOPC:
Windows update could not be installed because of error 2149842967 "" (Command line: ""C:\Windows\SysNative\wusa.exe" "C:\ProgramData\Package Cache\3ACBF3890FC9C8A6F3D2155ECF106028E5F55164\packages\Patch\x64\Windows8.1-KB2999226-x64.msu" /quiet /norestart")

02

Here is a hint to the solution: “Excel can’t start because api-ms-win-crt-runtime-l1-1-0.dll is missing”.

So it turns out that the Visual C++ Redistributable for Visual Studio 2015 silently fails to install on a fresh install of Windows Server 2012 R2 64 bit … So just update the OS and reinstall the Visual C++ Redistributable for Visual Studio 2015 update 1 from here:

https://www.microsoft.com/en-us/download/details.aspx?id=49984

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HOWTO make verbosity level accessible for users

LIBPF’s  4 diagnostic levels allow the model developer to fine-tune the verbosity at a global, compilation, unit, function and class instance level. Of these, two (verbosityGlobal and verbosityInstance) are also available at run-time, but normally not for the model user.

If you want to make them accessible to the user, there are several options. Here I’ll show you how to do it using a couple of real-valued Quantities that can be directly manipulated in the user interface or via the LIBPF™ Model User API.

NOTE: we use Quantities rather than Integers because currently there is no way for the user to change integers at runtime; the user will have to enter an integer value such as 1, 2 or 100 for really high verbosity.

Se here we go:

  1. declare two custom variables in your model class:
    Quantity global; ///< global verbosity
    Quantity instance; ///< instance verbosity
  2. initialize them in the model class constructor initializer list:
    DEFINE(global, "global verbosity", 0.0, ""),
    DEFINE(instance, "instance verbosity", 0.0, ""),
  3. register them in the model class constructor body:
    addVariable(global);
    addVariable(instance);
  4. make them user-modifiable in the setup method of the model class:
    global.setInput();
    instance.setInput();
  5. use them at model calculation to increase /decrease the verbosityGlobal and verbosityInstance variables, by implementing the FlowSheet::pre and FlowSheet::post overrides of your model class:
    void MyModel::pre(SolutionMode solutionMode, int level) {
      verbosityGlobal += global.toDouble();
      verbosityInstance += instance.toDouble();
    }
    void MyModel::post(SolutionMode solutionMode, int level) {
      verbosityGlobal -= global.toDouble();
      verbosityInstance -= instance.toDouble();
    }
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Qt Data Visualization preview

In the Qt Roadmap for 2016 they say “In addition, Qt 5.7 includes a lot of modules that have been previously available only with the commercially licensed Qt: … Qt Data Visualization – Versatile set of chart types for 3D visualization of data“.

This is interesting news: the Qt Data Visualization module provides a way to visualize data in 3D. What if we want to try it out now ? For example on Debian 8 which ships Qt 5.3.2 ?

Easy:

1. get and build QDV:

cd /tmp
git clone git://code.qt.io/qt/qtdatavis3d.git
cd qtdatavis3d
qmake
make

(the build of the library succeeds, while some example fails; we’ll skip on that).

2. build the Surface Example:

cd examples/datavisualization/surface
qmake
make

3. To run it, we need to make it find the right dynamic libraries:

find ../../.. | grep libQt5DataVisualization.so.5

this is easy with (on 32-bit systems, use /lib/ld-linux.so.2 rather than /lib64/ld-linux-x86-64.so.2):

/lib64/ld-linux-x86-64.so.2 --library-path ../../../lib/. ./surface

Mandatory screen-shot:
cc1

Note: to rotate, press the RMB (right mouse button) and drag.

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RSS feed for EASME news

If you are looking for the RSS feed of the EASME news (the European Commission’s Executive Agency for Small and Medium-sized Enterprises), here it is: http://libpf.com/easme.rss.

easme

For details how this works, see the related post RSS feed for AIChE ChEnected where we published scrapped the RSS feed of AIChE ChEnected (the online community of young professional chemical engineers hosted by the American Institute of Chemical Engineers)

Disclaimer: we do not alter in any way the contents of EASME news; we do not claim any rights on their content; we have no responsibility of their content; the service may break in the future; etc etc.

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A JSON-based file format for the exchange of thermo-physical model parameters

We present a proof-of-concept, JSON-based, vendor-independent file format for the exchange of thermo-physical model parameters. You can try it out in this browser-based demo tool.

We started from what is already avaiable: the IK-CAPE PPDX format, a vendor-independent file format for the exchange of thermo-physical property data and model parameters.

But although IK-CAPE PPDX was developed in 1997, it looks a lot like it’s still the 1970‘s:

sample IK-CAPE PPDX file

Its shortcomings are:

  1. It is a soup of data, thermo set-up and parameters; BTW for experimental data we now have ThermoML, an XML-based, IUPAC-backed standard;
  2. It’s ALL UPPERCASE !
  3. And it looks like it’s punched on a card: it is a text file, 80-columns wide, totally unstructured, write-your-own parser type of affair.

But then XML is so 2000-ish, so we propose to update IKC-PPDX adding a JSON format variant.

Also to make things tidier, we restrict it to the exchange of thermo-physical parameters, and we exclude data and thermo set-up.

Our proof-of-concept JSON-based file format divides the thermo-physical model parameters in four groups:

  1. Pure scalars, for pure component constant parameters
  2. Pure vectors, for pure component T and/or P dependent parameters
  3. Binary scalars, for binary constant parameters
  4. Binary vectors, for binary T and/or P dependent parameters

Here is the JSON schema.

And here is the simplest possible sample JSON file, with only one pure component scalar parameter:

{
  "components": [
    {
      "cid": "H2O",
      "name": "water",
      "cas": "1-11-111",
      "formula": "H2O"
    }
  ],
  "pure_scalar": [
    {
      "name": "PC",
      "parameters": [
        {
          "cid": "H2O",
          "value": 3800000
        }
      ]
    }
  ]
}

Get the JSON schema, the sample JSON files and the source code of the demo from the gitlab repo here.

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